Stallman would prefer that language distinguish between physical coercion and the kind of coercion that can take place because of a difference in knowledge or power (in this case, age). That's a fine point to discuss, but there are very considered reasons people use the same term - it's not just sloppy language.
Also, he'd prefer to assume a scenario where Epstein hid any coercion from his guests - which would make this a "an alleged but possibly unknowing sexual assault". I'm not sure what that's supposed to do to our discourse. Is everyone supposed to imagine the same scenario he does? Or the most expultory possible scenario? I think the uncertainty of the situation and presumption of innocence were already covered pretty well by "alleged".
The facts of the actual case are for the courts to sort out.
Stallman's focus on avoiding the factual label for the accusations is a weird priority, and there is nothing immature or irrational about calling it out.
I think it's fair to expect everybody to consider the possibility (and subsequently discount it for lack of credibility.)